Directed Self-Assembly (DSA) of block copolymers (BCP) using chemo-epitaxy is a patterning technique that allows the formation of regular gratings with resolutions below what is possible with current lithography tools. It makes use of spontaneous micro-phase separation of block copolymers (BCP). DSA is considered as one of the potential methods to obtain feature densities that cannot be obtained using actual optical techniques.
Optimally, the DSA technique used for generating particular gratings has a large processing window and is little or not sensitive to varying conditions. In order to define optimal materials, processing conditions and processing steps, the DSA technique typically at present is evaluated by studying gratings obtained with the DSA technique. More particularly, the order in the grating is qualified. The latter typically is done by manual classification of a series of Scanning Electron Microscopy (SEM) images of the grating, with a typical field-of-view of about 6 μm2. For this manual classification, for example, use is made of a discrete scale from 0 to 3 describing the amount of order in the grating. By way of illustration, FIG. 1 illustrates SEM images of DSA gratings as used for classification. In this example, the left-most image of the grating would result in a score of 0 and the most right figure would result in a score of 3. The score 0 represents complete disorder, while the score 3 represents prefect order.
The scoring is a manual task and thus operator-dependent and furthermore is time-consuming. In addition, to keep the evaluation feasible, the area probed is limited, and therefore the tests may still depend on the exact location that was probed with SEM.
Therefore, there is still room for improvement in scoring methods and devices for scoring the quality of DSA patterns.